Transport container

ABSTRACT

A transport container for transporting temperature-sensitive transport goods comprising a chamber for receiving the transport goods, a casing enclosing the chamber and at least one cooling element for temperature control of the chamber, wherein the cooling element comprises an evaporation element with a cooling surface, a desiccant for receiving coolant evaporated in the evaporation element and a reservoir for the coolant which is fluidly connectable with the evaporation element. Means are provided for evaporating the coolant stored in the desiccant and the desiccant is connected to the reservoir for transporting the vaporized coolant to the reservoir.

The invention relates to a transport container for transportingtemperature-sensitive transport goods comprising a chamber for receivingthe transport goods, a casing enclosing the chamber and at least onecooling element for temperature control of the chamber, wherein thecooling element comprises:

-   -   an evaporation element with a cooling surface,    -   a desiccant for receiving coolant evaporated in the evaporation        element,    -   a transport path for transporting the evaporated coolant to the        desiccant,    -   a reservoir for the coolant that is fluidly connectable with the        evaporation element.

When transporting temperature-sensitive transport goods, such as drugs,over periods of several hours or days, predetermined temperature rangesmust be met during storage and transport to ensure the usability andsafety of the drug. For various drugs storage and transport conditionsare prescribed that require temperature ranges from 2 to 25° C.,especially 2 to 8° C.

The desired temperature range can be above or below the ambienttemperature, so that either cooling or heating of the interior of thetransport container is required. If the environmental conditions changeduring a transport operation, the required temperature control includesboth cooling and heating. In order that the desired temperature range ispermanently and demonstrably adhered to during transport, transportcontainers with special insulation capacity are used. These containersare equipped with passive or active temperature control elements.Passive temperature control elements do not require any external powersupply during use, but use their heat storage capacity, and depending onthe temperature level a release or absorption of heat to or from theinterior of the transport container occurs. However, such passivetemperature control elements are depleted as soon as the temperatureequalisation with the interior of the transport container is completed.

A special form of passive temperature control elements are latent heataccumulators that are able to store thermal energy in phase changematerials, of which the latent heat of fusion, of solution or ofabsorption are much greater than the heat that they can store due totheir normal specific heat capacity. A disadvantage of latent heataccumulators is the fact that they lose their effect as soon as theentire material has completely gone through the phase change. However,by performing the reverse phase change, the latent heat accumulators maybe recharged.

Active temperature control elements require an external energy supplyfor their operation. They are based on the transformation of anon-thermal energy form into a thermal energy form. The release orabsorption of heat takes place, for example, in the context of athermodynamic cycle such as, e.g. by means of a compressionrefrigeration machine. Another embodiment of active temperature controlelements works on the basis of the thermoelectric principle, whereinso-called Peltier elements are used.

Therefore, the energy needed for the temperature control of a transportcontainer must be carried in the form of an electrical storage or of athermal storage. In the particular case of transport containers forairfreight, not only the volume, but also the weight and the ability ofbeing allowed, of the temperature control system including the energystorage, is of high importance. The cooling systems existing today oftenhave a large weight in relation to the insulation. The high weight inpassive cooling systems is due to the limited enthalpy, which, in theutilizable temperature ranges from 2-8° C., 15-25° C. and 34-38° C., isabout 200 kJ/kg. The energy density of accumulators required for activecooling systems is generally greater than 200 kJ/kg, but the maximumpermissible energy density for transport in aircraft is limited toapproximately 180 kJ/kg.

From WO 02/099345 A1 a transport container has become known, which isequipped with a passive temperature control element in the form of asorption cooling system. The cooling system comprises an evaporationelement with a cooling surface, a desiccant for absorption of thecoolant evaporated from the evaporation element, a transport path fortransporting the evaporated coolant to the desiccant and a reservoir forthe coolant that is fluidly connectable with the evaporation element. Asa coolant, for example, water is used, wherein the amount of heatrequired for the evaporation of the coolant is removed from thetransport goods that are to be cooled, the transport goods being cooledin this manner. Such a cooling system is inexpensive and has a lowvolume and a low weight. Already a comparatively small amount of coolantis sufficient to achieve a high cooling performance, because highamounts of energy are required for the evaporation of liquids, which aresignificantly higher than those for the phase transition from solid toliquid. The energy required to evaporate water at 8° C. is approx. 2.500kJ/kg. The absolute amount of water that air or a gas or a gas mixturecan absorb (100% relative humidity), depends heavily on the temperature.At a temperature of 30° C., 1 cubic meter of air can absorb 30 gr water,but at a temperature of 5° C. 1 cubic meter of air can only absorb about7 gr water. The evaporation rate and thus the cooling capacity can beadjusted by the following parameters: the water supply per unit time,the size of the evaporation surface and the relative water saturation ofthe surrounding gas. In order to achieve a low water saturation of thesurrounding gas, the gas loaded with the evaporated water is passed to adesiccant, which adsorbs the water. The desiccant is in this case onthat side of the cooling element, that shall emit the heat, and theevaporation layer is located on that side of the cooling element, onwhich cooling shall be achieved.

A disadvantage of the cooling system described in WO 02/099345 A1 isthat cooling no longer takes place as soon as the water is consumed orthe saturation of the desiccant is reached. The cooling can only becontinued when new coolant and a new desiccant are used. For largetransport containers, however, this is very complex and therefore notappropriate. For example, to cool a ship container for 30 days, about 18Wh/K are required. At a difference of 25K, a cooling capacity of 18Wh/K*25K=450 Wh is required. The pure evaporation of water requiresabout 694 Wh/kg; together with the desiccant an energy density for thesystem of about 347 Wh/kg results. Thus, for the autonomous cooling of aship container during a period of 30 days about 500 kg of water and 500kg of desiccant are required. Incidentally, a diesel engine would bemuch less weight efficient. It requires about 2-3 liters of diesel perhour, which would require a diesel tank of min. 1.440 liters.Furthermore, the weight of the aggregate itself as well as themaintenance and service costs must be considered.

The invention therefore aims to provide a transport container of thetype mentioned at the outset that has an improved cooling system. Inparticular, the cooling system is to be improved to the effect that thetransport goods can be kept in a predefined temperature range over alonger transport time without changing the weight of the cooling system,or that a weight and/or volume reduction of the cooling system can beachieved without reducing the maximum possible transport time,respectively.

To achieve this object, the invention essentially provides for atransport container of the type mentioned at the outset, whereby meansare provided for evaporating the coolant stored in the desiccant and thedesiccant is connected to the reservoir for transporting the vaporizedcoolant to the reservoir. In this way, the cooling element can berecharged. In the course of the cooling process, the cooling liquid, inparticular the water, evaporates, enters the desiccant and is heldthere. The recharging is accomplished by recuperating the cooling liquidfrom the desiccant and returning it to the reservoir, wherein thedesiccant releases the cooling liquid bound therein by causing it toevaporate. In this case, a preferred embodiment provides that the meansfor evaporating the coolant comprise a heating device and/or a devicefor reducing pressure, e.g. a vacuum pump. The heating device isdesigned, for example, to heat the desiccant to at least 120° C.,preferably to about 160-200° C. For this purpose, it can preferably beprovided that the heating device comprises heating coils extendingthrough the desiccant. The heating device can preferably be operatedelectrically.

The invention thus enables the realization of a closed circuit for thecoolant.

The evaporated coolant is preferably condensed on the way to thereservoir and passed in the liquid state in the reservoir. A preferredembodiment in this context provides that a line connectinq the desiccantand the reservoir is provided for transportinq the evaporated coolant.The line connecting the desiccant and the reservoir preferably has atleast one meander-shaped section, which serves as a condenser.

Instead of heating the desiccant, the release of the liquid from thedesiccant can depending on the desiccant also be effected by loweringthe pressure, in particular by generating a vacuum. Then between thereservoir and the desiccant a vacuum pump is used, which generates anegative pressure in the desiccant, whereby the bound liquid isevaporated. On the way to the reservoir, the pressure in the region ofthe condenser can be increased to liquefy the steam. The higher pressurekeeps the coolant in the reservoir in liquid form.

During the cooling process, the connection between the evaporationelement and the desiccant is opened while the recharge connectionbetween the desiccant and the reservoir is preferably closed. Forcharging the cooling element, the connection between the desiccant andthe reservoir is opened and the connection between the evaporationelement and the desiccant is preferably closed. In terms of design, itis therefore preferably provided that at least one shut-off device isarranged in the transport path for transporting the evaporated coolantto the desiccant. Furthermore, at least one shut-off device ispreferably arranged in the line connecting the desiccant and thereservoir.

The shut-off devices can be designed as valves, wherein the valves canbe controlled thermally or electrically or mechanically. The control canproceed in such a way that the heating of the desiccant is startedduring the ongoing cooling process and that the connection between theevaporation element and the desiccant is interrupted after the desiccanthas reached, for example, 100° C., wherein the connection of thedesiccant to the condenser or the reservoir is preferably opened at thesame time or a little later.

The charging can take place, for example, in a harbor or at anotherlocation where a power supply is available. For a complete drying orcharging of a system with 500 kg desiccant approx. 350 kWh are required,which needs about 28-35 hours with a power supply of 400V/32 A via a CEEconnection.

The variant with a vacuum pump or a heating in combination with a vacuumpump is significantly more energy efficient. With the same evaporativecooling performance, the energy consumption for the recuperation of thecoolant from the desiccant can be reduced by approximately 70-80%.

The cooling element can be integrated in various ways in the transportcontainer. For example, the evaporation element may be formed as a layerof a layered wall of the transport container. The evaporation elementcan thus be integrated either in one wall or in several walls of thecontainer. In this case, the evaporation element preferably forms theinnermost layer of the respective wall delimiting the chamber to betemperature-controlled. The evaporation elements or layers of theindividual walls can be connected via at least one channel with thedesiccant, wherein the desiccant is preferably integrated on or in oneof the walls of the transport container or arranged thereon at theoutside.

Alternatively, the cooling element (comprising the evaporation element,the desiccant and the reservoir for cooling liquid) may also be arrangedin a separate external housing, which is fastened to the transportcontainer as required. The chamber of the transport container to betemperature controlled and the evaporation element arranged in theexternal housing must then be connected via suitable channels with eachother, so that the air can be circulated.

The transport container according to the invention is also veryinteresting for air freight, since the system does neither requireelectricity nor batteries for the cooling during transport, but it canbe partially or fully charged with electricity or/and “coldness”.

In the period of charging the cooling element, the cooling is not inoperation, wherein a preferred embodiment of the invention provides thata second cooling system is arranged, which is built to cool the chamber,in which the transport goods are received, during charging of theevaporative cooling element. For this purpose, the transport containerpreferably comprises a latent heat accumulator, which communicates withthe chamber for heat exchange.

The latent heat accumulator can not only be used to bridge the chargingperiod of the evaporative cooling system, but can also be operatedsimultaneously with the same, resulting in a number of other advantages.The cooling capacity of the evaporative cooling system can be reduced sothat it can be made smaller and with less weight. The total coolingcapacity can be divided between the evaporative cooling system and thelatent heat accumulator. The cooling system can be designed so that whenthe performance of the evaporative cooling system is insufficient andthe temperature of the chamber increases, the additional cooling poweris obtained from the latent heat accumulator, which requires energy forthe phase transition from solid to liquid.

The cooling system may preferably be designed such that the phasetransition temperature (solid to liquid) of the latent heat accumulatoris chosen to be lower than the temperature resulting from the coolingcapacity of the evaporative cooling system. With the evaporative coolingsystem the temperature of the chamber can preferably be reduced to atemperature of 12-20° C., whereby the further cooling to a temperaturein the range of 2−8° C. is performed by means of the latent heataccumulator. Due to this combination the desiccant of the evaporativecooling system may be operated at a higher relative humidity, wherebythe amount of desiccant can be reduced. Also, the amount of latent heataccumulator can be reduced, since this only has to provide the energyfor cooling from the range of 12-20° C. to the range of 2-8° C.

Another advantage is that, in a partially charged (i.e. not fullycrystallized) latent heat accumulator, the same can be used to protectthe chamber from supercooling or to keep the chamber within the desiredtemperature range of, e.g., 2-8° C., when the outside temperature dropsbelow the level of the desired temperature range.

In a preferred embodiment, in which the transport goods are to be keptin the chamber at a temperature range of 2-8° C., the latent heataccumulator has a phase transition temperature of approx. 4-6° C.

If the transport container is stored in a refrigerated warehouse (e.g.in a customs warehouse) for a long time (e.g. for several days), e.g. ata temperature of 2-8° C., and the evaporative cooling system is set to acooling capacity so as to achieve a temperature lying above thetemperature prevailing in the refrigerated warehouse, the evaporativecooling system is not active during the storage period, so that nocoolant is consumed. Furthermore, the period of storage can be used tocharge the latent heat accumulator, which happens automatically in therefrigerated warehouse at a temperature of e.g. below 6° C., if thephase transition temperature of the latent heat accumulator is at 6° C.As a result, with minimal dimensioning of the two systems (latent heataccumulator and evaporative cooling system) a longer operation ortransport duration of the transport container can be achieved as if onlyone cooling system would be used alone.

Another advantage arises when the evaporative cooling system providesmore cooling capacity than required. The excess cooling power can thenbe used to recharge the latent heat accumulator, i.e. to have itreturned into the solid or crystallized state.

A preferred embodiment of the invention provides that the evaporativecooling system and the latent heat accumulator are arranged in cascadingmanner, i.e. that seen in the direction from the outside to the insideof the transport container first the evaporative cooling system iseffective and then the latent heat accumulator. The cooling surface ofthe evaporation element communicates therefore with the latent heataccumulator for heat exchange and the latent heat accumulatorcommunicates with the chamber for heat exchange. From a constructivepoint of view, this can preferably be realized in that the latent heataccumulator is arranged between the cooling surface and the chamber.

If the cooling capacity of the evaporative cooling system is set to atemperature above the phase transition temperature of the latent heataccumulator, a preferred embodiment provides that the cooling surfaceand the latent heat accumulator are separated by a thermal insulation.Although the cooling surface of the evaporation element and the latentheat accumulator then form a heat exchange connection, the heatexchange, however, is significantly slowed down by the thermalinsulation, so that there is a corresponding temperature gradient.

To ensure a safe operation of the evaporative cooling system, whereinthe relative humidity can be controlled independently of theenvironment, it is preferably provided that the cooling element issealed against the environment in a vapour diffusion tight manner. Theevaporated coolant is thus completely adsorbed in the desiccant, whereinthe cooling capacity may be adjusted in a simple manner by adjusting therelative humidity prevailing in the gas atmosphere of the evaporativecooling system.

Furthermore, it is preferably provided that the evaporation element andthe desiccant are separated by a thermal insulation. The thermalinsulation may be formed as an insulation layer arranged between theevaporation element and the desiccant, wherein the insulation layer canbe used as a transport path for transporting the evaporated coolant tothe desiccant. A preferred embodiment provides in this context providesthat the thermal insulation between the evaporation element and thedesiccant comprises an insulating layer that is permeable to vapourdiffusion, which forms the transport path.

Alternatively, the transport path may comprise at least one channelextending between the evaporation element and the desiccant.

Particularly suitable as desiccant are silica gels. These areinexpensive and can absorb up to 60% of their own weight of liquid,especially water.

The evaporation element advantageously comprises a textile, inparticular a felt, which contains the coolant, in particular water. Inprinciple, any material that has a large surface area is suitable.

With regard to the latent heat accumulator, one is preferred, the phasechange of which occurs in the temperature range of the desiredtemperature by the transition between solid and liquid or vice versa.Preferred phase change materials include paraffins and salt mixtures,such as, e.g., RT5 of the company Rubitherm or products from the companySasol.

Particularly preferably, the latent heat accumulator has a phasetransition temperature of 3-10° C., in particular 5° C., so that thechamber for the transport goods can be kept in a simple manner in atemperature range of 2-8° C.

The latent heat accumulator may preferably be formed as a plate-shapedelement. According to an advantageous embodiment the plate-shapedelement may comprise a plurality of in particular honeycomb-shapedhollow chambers, which are filled with the latent heat accumulatormaterial, wherein a honeycomb structural element according to WO2011/032299 A1 is particularly advantageous.

A particularly efficient temperature control is achieved according to apreferred embodiment, when the latent heat accumulator chamber surroundsthe chamber on all sides. Furthermore, it can also be provided that thecooling surface of the evaporation element surrounds the chamber on allsides.

In this context, it can be provided that the latent heat accumulator andthe evaporation element each form a layer of the shell of the transportcontainer.

The transport container according to the invention can in principle berealized in any dimensions.

The invention will be explained in more detail with reference toembodiments schematically illustrated in the drawing. Therein, FIG. 1shows an embodiment of the cooling system for a transport containeraccording to the invention, FIG. 2 shows a first embodiment of thetransport container with such a cooling system, and FIG. 3 shows asecond embodiment of a transport container with such a cooling system.

In FIG. 1, a cooling system is shown, which comprises an evaporativecooling system 1 and a latent heat accumulator 2. The evaporativecooling system 1 comprises an evaporation element 3, which is soakedwith a coolant, such as e.g. water, and has a cooling surface 4, and adesiccant 5 for receiving evaporated coolant from the evaporationelement 3. To supply the evaporation element 3 with coolant, the same isconnected to a reservoir 6. The transport of the evaporated coolant fromthe evaporation element 3 to the desiccant 5 is performed via a channel10. The common shell or wall of the evaporation element 3, the channel10 and the desiccant 5 is gas-tight, so that the relative humidity ofthe gas atmosphere within the evaporative cooling system 1 can beregulated independently from the environment. The evaporated coolant isabsorbed in the desiccant 5, which is e.g. a silica gel.

In that case the desiccant 5 is located on that side of the evaporativecooling system 1, on which heat is to be emitted, and the evaporationelement 3 is located on that (opposite) side of the evaporative coolingsystem 1, on which cooling is to be effected. On the heat-emitting sideof the evaporation element 3, a thermal insulation 7 is arranged.

On the cooling side of the evaporative cooling system 1, a plate-shapedlatent heat accumulator 2 is arranged, which is in heat exchangeconnection with the cooling surface 4 of the evaporative cooling system1 either directly or with the interposition of a thermal insulation (notshown). On the side of the latent heat accumulator 2 facing away fromthe evaporative cooling system 1, the chamber 9 to be temperaturecontrolled is arranged.

In the channel 10, a valve 8 is arranged, with which the connectionbetween the evaporation element 3 and the desiccant 5 can be opened orclosed. Furthermore, a channel 11 is provided, which connects thedesiccant 5 with the reservoir 6, to direct coolant, which wasrecuperated from the desiccant 5 by evaporation, in the reservoir 6. Forevaporating the coolant from the desiccant 5, a heating device 15 and/ora vacuum pump 14 is arranged. The vaporized coolant enters the channel11 and, with the valve 13 open, passes through the condenser 12, wherethe coolant is cooled, so that it is added to the reservoir 6 in itsliquid state.

FIG. 2 shows a cuboid transport container 16 in cross section, whosewalls are denoted by 17, 18, 19 and 20. The walls 17, 18, 19 and 20comprise a layer structure with an outer insulating layer 21 ofheat-insulating material and an inner layer 22, which forms theevaporation element. The evaporation element 22 is connected to thedesiccant 5 via a channel 10 extending through the insulating layer 21.Furthermore, a channel 11 is provided, which connects the desiccant 5with the reservoir 6, to direct coolant, which was recuperated from thedesiccant 5 by evaporation, in the reservoir 6. For evaporating thecoolant from the desiccant 5, a heater 15 is arranged. The evaporatedcoolant enters the channel 11 and, with the valve open (not shown),passes through a condenser (not shown), where the coolant is cooled sothat it is added to the reservoir 6 in the liquid state. The unitconsisting of the desiccant, the channel 11 and the reservoir 6 may bebuilt as a unit that is removable from the transport container 16 inorder to ensure easy attachment and removal.

In the embodiment according to FIG. 3, the cooling device comprising theevaporation element, the desiccant and the reservoir is accommodated inan external housing 24, which can be attached to conventional transportcontainers as required. FIG. 3 shows a cuboid transport container 23 incross section, whose walls are designated 25, 26, 27 and 28. The walls25, 26, 27 and 28 each comprise an insulating material 29 ofheat-insulating material. The wall 28 is provided with openings 30 and31, wherein a fan ensures that the air in the chamber 9 of the container23 is circulated, wherein the air is passed through the opening 31 tothe cooling unit 32 and the air cooled there is returned to the chamber9. The cooling unit 32 in turn comprises a meander-shaped evaporationelement 33, a desiccant 34, an insulating material 35 arrangedtherebetween and a reservoir 36 for the cooling liquid. The evaporationelement 33 is connected to the desiccant 34 via a channel 37 extendingthrough the insulation 35. Furthermore, a channel 38 is provided, whichconnects the desiccant 34 with the reservoir 36 in order to direct thecoolant, which was recuperated from the desiccant 34 by evaporation, inthe reservoir 36. For evaporating the coolant from the desiccant 34, aheater 39 is arranged. The evaporated coolant enters channel 38 and,with the valve open (not shown), passes through a condenser 40, wherethe coolant is cooled so that it is added to the reservoir 36 in itsliquid state.

1. A transport container for transporting temperature-sensitive transport goods comprising a chamber for receiving the transport goods, a housing enclosing the chamber and at least one cooling element for temperature control of the chamber, wherein the cooling element comprises: an evaporation element with a cooling surface, a desiccant for receiving coolant evaporated in the evaporation element, a transport path for transporting the evaporated coolant to the desiccant, a reservoir for the coolant which can be brought into fluid communication with the evaporation element, wherein means are provided for evaporating the coolant stored in the desiccant and that the desiccant is connected to the reservoir for transporting the vaporized coolant to the reservoir, characterized in that the means for evaporating the coolant comprise a vacuum pump, which is arranged in a line that connects the desiccant and the reservoir.
 2. The transport container according to claim 1, wherein the means for evaporating the coolant further comprise a heating device.
 3. The transport container according to claim 2, wherein the heating device comprises heating coils extending through the desiccant.
 4. The transport container according to claim 1, wherein the line connecting the desiccant and the reservoir has at least one meandering portion, which serves as a condenser.
 5. The transport container according to claim 1, wherein at least one shut-off device is arranged in the transport path for transporting the evaporated coolant to the desiccant.
 6. The transport container according to claim 5, wherein the at least one shut-off device is arranged in the line connecting the desiccant and the reservoir.
 7. The transport container according to claim 1, wherein the at least one cooling element is sealed against the environment in a vapour diffusion tight manner.
 8. The transport container according to claim 1, wherein the transport container further comprises a latent heat accumulator, which communicates with the chamber to exchange heat.
 9. The transport container according to claim 8, wherein the cooling surface is connected with the latent heat accumulator to exchange heat and that the latent heat accumulator is connected with the chamber to exchange heat.
 10. The transport container according to claim 8, wherein the latent heat accumulator is arranged between the cooling surface and the chamber.
 11. The transport container according to claim 8, wherein the cooling surface and the latent heat accumulator are separated from each other by a thermal insulation.
 12. The transport container according to claim 1, wherein the evaporation element and the desiccant are separated from each other by a thermal insulation.
 13. The transport container according to claim 1, wherein the transport path comprises at least one channel extending between the evaporation element and the desiccant.
 14. The transport container according to claim 12, wherein the thermal insulation arranged between the evaporation element and the desiccant comprises an insulating layer that is permeable to vapour diffusion and which forms the transport path.
 15. The transport container according to claim 8, wherein the latent heat accumulator has a phase transition temperature of 3-10° C.
 16. The transport container according to claim 1, wherein the evaporation element comprises a coolant receiving textile.
 17. The transport container according claim 16, wherein the coolant comprises water and wherein the textile comprises a felt.
 18. The transport container according to claim 4, wherein at least one shut-off device is arranged in the line connecting the desiccant and the reservoir.
 19. The transport container according to claim 9, wherein the latent heat accumulator is arranged between the cooling surface and the chamber.
 20. The transport container according to claim 11, wherein the evaporation element and the desiccant are separated from each other by a thermal insulation. 